The invention relates to a photoelectric detection device comprising a vacuum chamber provided with a window having a substrate which bears a photocathode on the internal surface of the vacuum chamber. The device is sensitive to incident luminous radiation between a short wavelength bottom threshold .lambda..sub.1 and a longer wavelength upper threshold .lambda..sub.2, with the electrons emitted by the photocathode being focused, accelerated and deflected by electronic means to deliver signals or an image representative of luminous events projected onto the photocathode.
The invention also relates to tubes using this type of photoelectric detection device such as image dissector tubes, and in a general manner all image reproduction tubes for which localised errors in reproduction are to be eliminated.
This aspect of localised errors is of considerable importance in image dissector tubes. These tubes are generally designed to detect punctiform events appearing in a field of vision, principally a scanning of the sky, such as in the observation of clouds or particles in meteorology or in the tracking of stars in astronomy. The image detected by such a tube thus appears in the form of a fairly uniform image in which the events to be detected appear in very small dimension in relation to the total extent of the image. In this image, however, there are also faults which can be mingled with the events to be detected or hinder their detection and which thus detract from the efficiency of the dissector tube.
A dissector tube generally comprises a vacuum chamber provided with a window having a photocathode which emits electrons on the incidence of luminous radiation. The scene to be analysed is projected optically onto the inlet window. The electrons emitted by the photocathode are accelerated, focused and deflected by suitable electron optics onto an electron multiplier having a very small aperture at its entrance. By a system of electronic scanning, the electrons emitted by each point of the image formed on the photocathode penetrate the multiplier which reproduces an electrical signal by conventional electronic means, which can be displayed on a screen or utilised to position the dissector tube.
When the image bears the faults previously mentioned, these may result in a faulty perception of the image or difficulties in positioning the dissector tube, as the fault may take the place of the event in question in the image field, and thus control the enslavement of the dissector tube.
Such a dissector tube is described in the publication entitled: "The Image Dissector as an Optical Tracker" by E. H. Eberhardt published in the "Proceedings of the seminar on optical tracking systems, El Paso, Tex., U.S.A., Jan. 18-19th, 1971.
A dissector tube is described therein which is used for the tracking of stars. In the image field obtained on the photocathode the star appears in the form of a luminous point. For these applications, it may be necessary to detect variations in position on the scale of one micron on the photocathode. It happens very often that faults can be confused with the luminous event to be detected and followed. These tend to be caused by sudden variations in sensitivity, at a short distance, between an image point and a neighbouring image point, creating the most disastrous distortion.